Aviation motor fuel



Patented ct. 14, 1947 UNITED STATES PATENT OFFICE AVIATION MOTOR FUEL Thomas B. McCulloch, Baytown, Tex., assignor to Standard Oil Development Company, a corporation of Delaware No Drawing. Application April 1, 1944,

- Serial No. 529,163

7 Claims.

. 1 The present invention relates to a motor fuel composition suitable for employment as an aviation fuel under rich mixture or take-off conditions or conditions in which the aviation motor is rapidly accelerated. More particularly this invention is concerned with a fuel composition comprising a major portion of an isopa'rafilnic hydrocarbon, an organo-metallic anti-detonant, anda minor portion of a saturated ester of an aromatic carboxylic acid.

The dwindling natural resources of petroleum and the deficiency of many countries in these resources have lead many investigators to search for adequate substitutes for the petroleum hydrocarbons as motor fuels; thus, for example, the alcohols, the ethers', and the aliphatic esters of the. mono carboxylic acids have beensuggested as motor fuels either alone or in conjunction with the hydrocarbons. These afore-mentioned compounds have been satisfactory to some extent in the ordinary motor, but are usually unsatisfactory in performance in the aviation motor. Genas cruising conditions in the air craft industry. The motor fuel composition of my invention contains preferably isoparaflins, either synthetically produced or naturally occurring and an ester of an aromatic mono carboxylic acid. In addition, the fuel may contain catalytically cracked naphthas, xylidines, tetraethyl lead and other anti-detonants in my composition will depend to'some extent on the composition of the fuels with which it is used, but usually it should not exceed of the fuel composition; and, under ordinary circumstances, as little as 5 to 10% will be suitable.

. The hydrocarbon component generally should comprise from 75 to 95% of the finished fuel and usually will be made up of the branched.

chain hydrocarbons as typified by the isomers of the hexanes, heptanes; octanes,'nonanes and the like. The branched chain paraffin hydrocarbons may be'obtained by the precise fractionation of crude petroleum fractions or they may be proerally the amounts of thevarious non-hydrocarbon compounds which are added to increasethe anti-detonant property of thefuel is so large thatthe other characteristics suffer. Furthermore these compounds are not particularly suitable as an aviation fuel when employed under take-off conditions or under conditions which require rapid acceleration of the motor.

I have now discovered that a class of compounds exist that upon addition to aviation motor fuels comprising substantially the isoparafiln hydrocarbons give unusual performance under rich mixture conditions. This class of compounds may be broadly defined as the esters of these last mentioned compounds are not as effec duced syntheticallyby the well known alkylation technique in which an olefin is reacted with an isoparaflln.

Suitable anti-detonants; such as tetraethyl lead in an amount usually between 3 and 6 cc. of tetraethyl lead for each gallon of fuel, may be employed. but smaller amounts may be used.

Likewise, other anti-detonants such as iron carbonyl and the xylidines may be used. While tive as the tetraethyl lead, small concentrations the aromatic carboxylic acids having 8 to 12 carbon atoms in the molecule and boiling in the range between 390 and 510 F. As examples of the types of compounds suitable for employment in the present invention may be mentioned methyl benzoate, ethyl benzoate, butyl benzoates, propyl benzoate,'isoamyl benzoate and the methyl and ethyl esters of the toluic acids.

While prior investigators have found that the esters of the aromatic carboxylic acids have no beneficial efiect on the anti-detonating properties of fuels, unexpectedly I have discovered that these compounds as exemplified by ethyl benzoate and the like give unusual performance as aviation motor fuels under rich mixture conditions; while in line with the findings of the prior investigators they are generally unsatisfactory under lean mixture conditions or what is known since one of theparticular advantages of the fuel of the present invention is its low vapor pressure which eliminates the fire and explosion hazard usually encountered in most aviation fuels. The high boiling points of the esters of the aromatic carboxylic acids assures a fuel resistant to formation of explosive mixtures provided a hydrocarbon fraction of high boiling .point and low vapor pressure is used therewith. It is, therefore. contemplated that the vapor pressure of my pre- The amount of ester employed It was determined by calculation that the blendferred fuel composition will be about 4 pounds or less as measured by the Reid vapor pressure method. a In order to illustrate further the unique propof methyl benzoate, ethyl erties of my preferred composition, 95% of'a 5 hydrocarbon fuel having 9. Reid vapor pressure of 4.3 pounds, which was made up by blending suitable amounts of isobutane-butylene alkylate with isohexane and isoheptane, was blended with. 5% of ethyl benzoate and the fuel resulting was leaded with 4 cc. of tetraethyl lead per gallon. On testing this fuel composition by the AN AFD 3-0 rich mixture method an indicated mean effective pressure of 190.? pounds was obtained.

unexpected in the light, of prior octane number determinations which showed an average blending value of only 60 for the ethyl benzoate in the aviation base fuel mentioned: The octane numbers were determined by the Tentative Method of Test for Knock Characteristics of Aviation Fuels according to the A. S. T. M. Designation:

It will be apparent to the skilledworker that the aviation composition of my invention gives surprisingly good performance-in the aviation motor under rich mixture conditions. A fuel having an I. M. E. P. of 190 or better has been shown by actual motor operating conditions to give very satisfactory performance; onthe other hand, one having an octane number of 60 gives poor per-- formance under cruising conditions. It is therefore contemplated that my aviation fuel composiesters in my composition, it is within the spirit -4 and scope of my invention to employ mixtures of the esters. For example, I may employ the ethyl esters of the toluic acids in my composition or a mixture of methyl and ethyl benzoate with equally good results as when a single as ethyl benzoate is used.

The nature and objects ofthe present invention having been fully described and illustrated, what I wish to claim as new and useful and to secure by Letters Patent is:

1. An aviation motor fuel comprising a major portion of a high boiling isoparaihnic hydrocarbon of high anti-knock value and a minor portion of a saturated alkyl ester of the group consisting ester such ate, propyl benzoate, iso-amyl bcnzoate, methyl ester of toluic acid and ethyl ester of toluic acid. 2. An aviation motor fuel in accordance with claim 1 in which the alkyl ester is ethyl benzoate. 3. An aviation motor fuel suitable for operation under rich mixture conditions in an aviation motor which comprises a major portion of a high boiling isoparamnic hydrocarbon, a minor portion of a saturated'alkyl ester of the group consisting of methyl benzoate, ethyl benzoate, butyl benzoate, propyl benzoate, iso-amyl benzoate. methyl ester of toluic acid and ethyl ester of toluic acid and an. organo metallic anti-detonant. 4. An aviation motor fuel comprising a major portion of a high boiling isoparafllnic hydrocarbon having no less than 6 carbon atoms in the molecule, and a minor portion of a saturated alkyl ester of the group consisting of methyl benzoate, ethyl benzoat-e, butyl benzoate, propyl benzoate, iso-amyl benzoate, methyl ester -of toluic acid and ethyl ester oftoluic acid.

5."An aviation fuel which comprises from '15 to of a high boiling isoparafllnic hydrocarbon of. high anti-knock value and having 6 or more carbon atoms in the molecule and from 5- to 25% of a saturated alkyl ester of the group consisting of methyl benzoate, ethyl benzoate, butyl benzoate, propyl benzoate, lso-amyl benzoate, methyl ester of tolulc acid and ethyl ester of toluic acid.

. 6. An aviation fuel in accordance with claim 5 in which the vapor pressure is, less than four pounds. I

7. An aviation motor fuel suitable for employment in an aviation motor under rich mixture conditionswhich comprises isoparamnic hy'drocarbons having 6 or more carbon atoms in the molecule, tetraethyl lead, ethyl benzoate, and xylidine.

THOMAS B. MCCULIOCH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Endo, Journal of Fuel Society, Japan, vol. 11, May 1932, pages 564-574.

benzoate, butyl hence-- 

